1. Field of the Invention
The present invention relates to a method of producing a liquid ejection head.
2. Description of the Related Art
Generally, an ink jet recording head applied to an ink jet recording system includes a fine ejection orifice, a liquid flow path, and an ejection energy generating element provided in part of the liquid flow path. A known example of a method of producing the ink jet recording head is a method described in Japanese Patent Application Laid-Open. No. 2007-160625.
In the production method disclosed in Japanese Patent Application Laid-Open. No. 2007-160625, first, an ink flow path is formed on a substrate by photolithography technology, and then the rear surface is subjected to grinding or polishing, followed by forming an etching mask from a double layer of a metal oxide film and an organic resin film. After that, an ink supply port is formed by chemical etching from the rear surface of the substrate, thereby producing an ink jet recording head.
However, the method described in Japanese Patent Application Laid-Open. No. 2007-160625 uses, as an etchant for chemical etching of silicon, a very highly reactive chemical, such as tetramethylammonium hydroxide (TMAH), KOH, HF, and HNO3. The etching mask is therefore required to have high chemical resistance so as not to be impervious to such chemicals. However, in order to form a film having high chemical resistance, it is generally necessary to form the film at high temperature of about 300° C. or more in either case of an inorganic film or an organic film.
Meanwhile, in order to thin the silicon substrate, the silicon substrate is subjected to grinding to a thickness of 80 μm, for example, by a machine or the like. At this time, a crushed layer (affected layer) is generated on the ground surface of the silicon substrate. Conventionally, the affected layer is removed by polishing, wet etching, or other methods.
However, the method of removing a crushed layer by wet etching cannot control the shape of a peripheral end portion of a wafer and may lower the covering property (coverage) of an organic film.
To address the problem, the method of removing a crushed layer by polishing has been proposed in the conventional method. However, in the case of removing a crushed layer by polishing, the crystal structure may be damaged by polishing and crystal distortion may occur in the polished surface. If a damaged layer including crystal distortion is present on an etching surface, when an ink supply port is formed by anisotropic etching, the etching may progress irregularly because of the damaged layer, with the result that the ink supply port may be formed into an abnormal shape.
In the conventional method, a method of removing a crushed layer by dry etching has also been proposed. However, in the method of removing a crushed layer by dry etching, depending on gas species or the type, the rate of etching the crushed layer may be accelerated or surface deposition may occur, which enlarges a grinding mark generated during grinding. If the grinding mark is larger, the film forming property of the surface is lowered, and thus the mask performance of the etching mask may be lowered.
Further, when the grinding mark is removed by an etchant to flatten the surface, the bevel profile of a peripheral portion of the silicon substrate may be distorted. As a result, the covering property of the etching mask used for crystal anisotropic etching may be lowered at the peripheral portion of the silicon substrate, and thus the peripheral portion of the silicon substrate may be fractured by etching.
Further, when the grinding mark or the crushed layer is removed by polishing to flatten the surface, a damaged layer is generated. In the case where the damaged layer is removed by a chemical dry etching apparatus, the etching rate increases selectively at a portion of the damaged layer where damage occurs. Examples of the damage include crystal distortion and a polishing mark.